1. Field of the Invention
This invention relates generally to video signal recording and/or reproducing apparatus and, more particularly, is directed to improvements in such apparatus of the type in which, before recording with frequency or other angle modulation, the video signal is pre-emphasized and clipped, and, on reproduction, the reproduced signal is demodulated and then de-emphasized.
2. Description of the Prior Art
It is well known to record information signals, such as video signals, on a magnetic tape or other recording medium. In the case of video tape recorders, when recording color video signals which include a luminance component and a chrominance component, it is known to separate such components and then to frequency modulate the luminance component on a carrier having a relatively high frequency. However, the level of the FM noise signal increases with the frequency of the carrier of the frequency modulated luminance component in a recording and reproducing system using a magnetic tape and a magentic head, so that, if a high carrier frequency is employed, the FM noise signal has a correspondingly high level.
In this regard, in order to compensate for the level of the FM noise signal, prior art systems have pre-emphasized the luminance component of the video signal prior to recording to reduce the influence of such noise. However, when the amount of emphasis provided by the pre-emphasis circuit is increased for the purpose of eliminating the high level FM noise signal, relatively large overshoots are produced at those portions of the video signal where the level of the latter is abruptly changed, that is, large overshoots are produced at the rise and fall portions of the video signal due to the pre-emphasis. When the emphasized video signal with such large overshoots is employed as the modulating signal for the frequency modulation, frequency shifts corresponding to such large overshoots result in overmodulation and are too great to be included in the transmission band of the apparatus, that is, the band of frequencies that can be magnetically recorded and reproduced, so that the recording and reproducing of the video signal cannot be effected with a linear characteristic. In order to bring the frequency modulated video signal, as recorded and reproduced, within the transmission band, existing recording and reproducing apparatus are provided with a white clip circuit which limits the pre-emphasized video signal at a predetermined level so as to clip some of the overshoots prior to the frequency modulation of the carrier with the pre-emphasized video signal or its luminance component.
In the case of such limiting of the pre-emphasized luminance component of the video signal, however, even if the video signal is processed in a de-emphasis circuit, after demodulation, during the reproducing operation, it is not possible to obtain precisely the original video signal owing to the distortion of waveforms at the limited or clipped overshoot portions. More particularly, because of such clipping, the portions of the reproduced signal greater than the predetermined level are lost, resulting in a lengthening of the rise time between the rise and fall portions of the video signal, that is, the black and white portions of the video picture. As a result, a dull picture results in which black picture lines run onto adjacent white areas, causing so called smear around the peripheral portions of the black areas.